Electronic communication devices such as portable phones usually comprise at least one antenna to transmit and receive electromagnetic signals. Antennas, which are external to the electronic communication device, tend to provide superior radiated performance to antennas which are internal to the electronic communication device. External antennas are often retractable into the electronic communication device to reduce the size of the device and to reduce the likelihood that the antenna may be damaged by a user.
When an external antenna is in a retracted position, it may be unable to transmit and/or receive electromagnetic signals. Therefore, electronic communication devices which comprise an external antenna usually also comprise a second antenna so that when the external antenna is retracted, the second antenna may transmit and receive electromagnetic signals.
One problem associated with electronic communication devices which comprise more than one antenna is that the antennas interfere with one another, either through direct electrical connection or through electromagnetic coupling.
Another problem associated with electronic communication devices which comprise more than one antenna is that it is difficult to achieve similar impedances in each of the antennas over more than one operational frequency band using the same feeding circuit.
A further problem associated with electronic communication devices which comprise more than one antenna and have a plurality of physical configurations (e.g. a portable fold telephone or a portable slide telephone) is that the impedance of each of the antennas changes significantly depending on the physical configuration of the electronic communication device. Consequently, the radiative performance of each of the antennas changes significantly depending on the physical configuration of the electronic communication device.
Some antenna arrangements address the problem of electromagnetic interference by providing physical separation between the radiating portions of the antennas. One disadvantage associated with this solution is that in order to provide physical separation, external antennas usually have a long insulating cap and consequently, a reduced electrical length which reduces the radiation performance of the external antenna. If a person wishes to increase the electrical length of the external antenna it may be necessary to increase the size of the electronic communication device to ensure that there is physical separation between the radiating portions of the antennas.
Other antenna arrangements address the problem by using switches (mechanical or electrical) to disable the external antenna when it is retracted and to disable the internal antenna when the external antenna is extended. One disadvantage associated with this solution is that switches are usually expensive. Furthermore, mechanical switches are usually unreliable and electrical switches may introduce non-linearity problems.
Therefore, it is desirable to provide an alternative antenna arrangement for electronic communication devices.